How big screws for 12mm ply? I want to make some simple toy boxes out of 12mm ply (1/2”) but how big screws and how thick ? heres a chart of Gauge to thickness http://freespace.virgin.net/matt.waite/resource/handy/screwsize.htm ill make a post if and when I make them xD and I want countersunk them flush with the plywood and if any one knows what the BLACK coloured screws because most of the screws at my home deport store are yellow Zink platted and I think black screws will look nicer xD

15 replies so far

If I envision what your wanting to do correctly I wouldn’t use screws at all in something that thin in plywood, they would only weaken the wood and wouldn’t add any strength. I would use glue and brads, or a pin nailer. If you need more strength. You could build a frame inside the box of strips 1/2-3/4” square and than use #6 screws thru the ply into the frame. A ply box though, your screw is going into the end of a piece and it going to be rather thin and fragile. How big are these toy boxes, if we are talking footlocker size a better design would be to use frame and panel construction. Use screws on the Frame if you want, though I wouldn’t do that either.

No matter what you need to glue the joints. I don’t have a Brad nailer so I use trim screws instead like these: http://low.es/19ODT7q

The description is wrong in the link. They are #6×1-5/8”. They won’t add a lot of strength but they will hold the joint while the glue sets. Get those or 1-1/4”. You must drill a pilot hole but don’t countersink it. The heads are very small and don’t need countersinking.

If you’re planning on using screws from the face of one panel into the edge of the next, you’ll want something very thin and long. It is also a good idea to pre-bore the holes to keep the point of the screw from driving the plys apart as the screw advances. If you have the ability, you could make oversized box joints that would require glue alone and still offer great strength.

I agree with just using brads if you need to use anything. I think one of these joints would work better, if you like the black screws, you could peg the rabbet joint with walnut dowels. These 3 are quick and easy to cut on the tablesaw. You said you’re making multiple boxes, so you could cut all the similar joints at the same time. I think you’ll find these will hold up longer than screws. Toy boxes take a beating, and the screws are sure to work themselves loose.

Rabbet

Rabbet/Dado

Locking rabbet

-- - The mightiest oak in the forest is just a little nut that held its ground.

The general rule of thumb is to use 3x the thickness of the material being used, so in your case, 1 1/2” screws. In reality though, I go for about an inch into the work piece being attached. I’m not sure of a chart for length, but there’s some floating around that have info on the different screw sizes (#6, #8, etc.).

This is where drywall screws work well. They have a thin shank, so won’t cause the plywood to delaminate. Another thing you have to consider is what type of plywood are you using? If it’s Baltic Birch (I’m assuming it is BB because of the mm designation), fine, but if you are using 4 or 5 ply domestic plywood, I wouldn’t count on screws keeping the pieces aligned, even with a pilot hole. When you drill a pilot hole, the drill bit will drift toward the softer ply. You can never get the pieces to line up perfectly. A brad nailer is the best tool to use, but since you don’t have one, I have no other suggestion. The rabbet/dado joint is probably your best solution, relying on glue and surface area for strength.